Thayne Ormsby, 21, was found guilty by a jury of seven men and five women on three counts of murder and one count of arson on Friday afternoon.

Ormsby, an Ellsworth native who was living in Orient in 2010, pleaded not guilty and not guilty by reason of insanity in connection with the stabbing deaths of Jeffrey Ryan, 55, Ryan’s son Jesse, 10, and Ryan family friend Jason Dehahn, 30, all of Amity, on June 22, 2010. They were found dead about 27 hours after the killings at the Ryans’ home on U.S. Route 1, according to police. The arson charge stems from Ormsby burning the elder Ryan’s truck after the slayings.

On Tuesday, the jury will hear evidence as to Ormsby’s state of mind at the time of the crime. Jurors then will be asked to determine whether Ormsby was criminally responsible for his actions.

That defense is being used more often in Maine, according to information from the state and some attorneys.

Data from the State Forensic Service in 2010 showed that since 1946, a total of 118 people had been deemed not criminally responsible by reason of insanity for crimes ranging from impersonating a public servant to murder. The State Forensic Service is an arm of the Department of Health and Human Services.

State Deputy Attorney General William Stokes, who is prosecuting the Ormsby case, would not comment on an ongoing case. But in a March 2010 Bangor Daily News article he said that not criminally responsible pleas were “very rare” before 2000, and when used were seldom successful.

Such pleas are seen more often now, however, particularly in murder cases.

Between 2000 and 2010 in Maine, for instance, 12 defendants charged with murder pleaded not criminally responsible by reason of insanity. In seven of those cases, prosecutors agreed with recommendations of state and defense psychiatrists, sending the defendants to the Riverview Psychiatric Center in Augusta rather than trial.

Juries decided only two of those 12 cases, rejecting one and deadlocking in the other case in which the defendant later pleaded guilty to manslaughter.

The director of the State Forensic Service in 2010, Dr. Ann LeBlanc, said in that same BDN article, “Our best estimate is that insanity is raised in 2 to 4 percent of cases in Maine and successful about 25 percent of the time.”

Two insanity defenses have been offered in Aroostook County since 2000, and one was successful.

Michael McDonald, who killed his father, Michael W. McDonald, in Masardis in 2004, was found not guilty by reason of insanity that same year.

The elder McDonald was found dead in his Masardis home. The state medical examiner’s office said that he died of a shotgun wound, blunt force trauma to the head and multiple stab wounds.

In 2006, Christopher Shumway, 20, was found guilty and criminally responsible for the grisly January 2005 murder of 20-year-old Erin Sperrey, his supervisor at a Caribou Tim Hortons doughnut shop.

During a jury-waived trial, Aroostook County Superior Court Justice E. Allen Hunter found Shumway guilty of murder, gross sexual assault involving Sperrey, and robbery of the restaurant. Hunter said that Shumway was not insane at the time of the death nor during his subsequent actions.

Melanie Dutra, one of Jeffrey Ryan’s daughters and Jesse Ryan’s sister, said that she never has believed that Ormsby is insane. She noted on Friday that he was well enough mentally to plan the crime and to destroy evidence. Ormsby made a list of two individuals that he wanted to kill, one of whom was Jeff Ryan. He also burned his clothes after the killings and threw the knife used in the murders into a nearby bog.

“He had enough sense to cover up the crime and to flee,” she said on Friday. “To me, those are not the actions of someone who is insane.”

To have a successful insanity plea under the law, a defendant must have documented mental health problems, prove he or she was psychotic at the time of the crime and also show that he or she was unable to determine the difference between right and wrong.

If the jury accepts Ormsby’s plea, he would be sent to the Riverview Psychiatric Center in Augusta for an undetermined amount of time. If jurors find him sane, Ormsby faces a sentence of between 25 years and life in prison on each of the murder charges. He also faces up to 30 years in prison on the arson conviction.

Judges are allowed to impose life sentences in Maine under specific circumstances. One of them is being convicted of multiple murders.